"First-in-the-World" Project Unveiled

July 6, 2012

SEPTA Introduces New Model for Wayside Energy Storage

For nearly 100 years, SEPTA's Letterly Substation in Kensington has been powering a portion of the Market-Frankford Line. On June 27, 2012, SEPTA officially unveiled a new device that will turn the facility into a cutting edge home of an emerging power technology for years to come.

That technology is called "wayside energy storage," and it has the potential to transform energy-consuming trains into rolling power generators. Made possible by a $900,000 grant from the Pennsylvania Energy Development Authority (PEDA), SEPTA partnered with Philadelphia-based smart grid firm Viridity Energy to design and implement a storage system to capture, store, and reuse "regenerative energy" created by braking trains.

In reality, regenerative braking energy in and of itself is not a new technology. Hybrid-electric vehicles, such as the Toyota Prius and 472 of SEPTA's buses, have for years used regenerative braking to charge on-board batteries and reduce fuel consumption by reusing the stored energy upon acceleration. Even trains, including SEPTA's Market-Frankford Line, come equipped with "regen" capabilities to provide additional power to the propulsion system for nearby accelerating trains to use.The problem for trains, however, is that if there is not a nearby train accelerating to accept the regen, the energy is wasted - dissipating through the train's resistor banks as heat. Replicating the hybrid technology would require a way to store the otherwise wasted energy.

The transit industry's solution was the same as the automotive industry: a battery. SEPTA's system happens to be comprised of several large batteries - produced by Saft Batteries, Inc. - and a controller - produced by ABB Envitech, Inc. - and is stored in an offsite ("wayside") location, but it serves essentially the same purpose: to capture, store, and reuse regenerative braking energy. And, in the same way that SEPTA's hybrid buses reduce fuel consumption, SEPTA anticipates that the battery will reduce its electric bills at Letterly by 10 percent, or approximately $190,000 per year.

The Battery Installed at Letterly Substation

So the most groundbreaking feature of the project is not its potential for energy savings. Rather, it is the other ways the storage system will be simultaneously put to use. Through its partnership with Viridity Energy, SEPTA will participate in the "frequency regulation" market, which is managed by PJM Interconnection to keep the electric grid in a perpetual state of equilibrium. SEPTA's battery will provide PJM with an on-call source of energy to help ensure grid stability. PJM will pay a premium for this service: SEPTA anticipates that frequency regulation and other demand response (load-shedding) programs could generated up to $250,000 per year in new revenue.

This new source of revenue is the game-changer for wayside storage, which in the past has depended on subsidies to support the capital investment in a technology whose return (energy savings) failed to recoup the upfront cost. With the value added by smart grid technologies to tap into frequency regulation and demand response markets, there is now a stronger business case for large energy consumers like SEPTA to pursue the technology to achieve both environmental and economic sustainability goals.

More importantly, the strengthened business case creates scalability, and with it, a potential compounding effect of the technology's environmental and economic impact. For its part, SEPTA has more than 30 substations that service its propulsion-powered transit system, many of which could house a wayside storage devices like the one at Letterly. In fact, SEPTA recently received a $1.44 million grant from the Federal Transit Administration (FTA) to install a second storage device at the Griscom Substation in Northeast Philadelphia. The FTA grant will also be used to test the viability of an alternative battery technology to determine the best fit for SEPTA's propulsion system. The results of this test will be made available to the industry so that other rail transit agencies can make better informed decisions about how wayside storage fits into their own systems.

Scaling wayside storage will take time. For now, Letterly is live, and the battery is off to work providing benefits to customers and taxpayers by reducing costs and improving operational efficiency. Ultimately, the project is indicative of SEPTA's broader approach to sustainability: pursuing innovative projects that use existing assets to achieve performance goals while bolstering the bottom line. In doing so, SEPTA has taken a proven technology and created a more sustainable and replicable implementation model for the transit industry to follow.